Multiplex telegraphy.



PATENTED MAY '7, 1907.

J. BURRY. MULTIPLEX TBLBGRAPHY.

APPLIOATION FILED JAN.21,1906.

1 9 Elm-us 11 ['0 z JOHN BURRY, OF RIDGEFIELD PARK, NEW JERSEY. v

MULTIPLEX TELEGRAPHY.

Specification of Letters Patent.

Patented May 7, 1907.

Application filed January 21, 1905. Serial No. 242,089.

To to whom it may concern:

- Be it known that I, JOHN BURRY, a citizen of the United States, residing at Ridgefield Park, in the county of Bergen and State of New Jersey, have invented certain new and useful Improvements in Multiplex Telegraphy, of which the following is a specification, reference being had to the drawing accompanying and forming part of the same. Among the various systems of so-called multiplex tele raphy now extant none that I am aware o has been found. successful in. practice, for long distance work, at least. Those systems which contain the elements of practicability are frequently limited in their application by defects inherent in their principle of operation. For example, the well known system in which at thetransmitter the current over the line wire is divided by means of a rotating member which makes contact successively with a number of insulated contacts connected with as many circuit controlling keys or devices, the receiving end of the line being equipped with ap paratus working in unison with the transmitter, is subject to serious drawbacks in at least two particulars; first, the difficulty of securing the necessary absolute unison or synchronism in the moving parts of the transmitting and the receiving devices, and second, in the minute subdivision of the current when any considerable number of transmitting and receiving devices are connected on the same line. In the latter case the time interval between successive connections of the moving current-distributing member with the same transmitting devices is too long for successful operation that is, the

' substantial continuity of the current between a particular transmitting device and its receiveris impaired to such an extent that the difierentiation of Morse dots, dashes, and spaces is practically impossible. In other words, the break in the current, from the instant the moving member leaves a given contact until it returns to the same,

occupiesso long a time that the receivingv apparatus connected with the corresponding contact at the other end of the line is affected thereby; Whereas the makes and breaks/of the currentby the uniformly-moving member should follow each other in such. rapid succession that the receiving device will not be appreciably affected, but be able to respond to the make and break of the corresponding transmitting key in substantially the same manner as if the current between the two were otherwise continuous.

The difficulty already mentioned, of maintaining absolute unison between the moving contacts at the two ends of the line, frequently becomes an impossibility, and hence an insurmountable obstacle to the successful 1 operation of the system. This is es ecially apt to be the case when the number 0 instruments connected with the same current distributing apparatus is considerable, as in the instance ust described. Here a very slight departure from perfect synchronism may throw the system into hopeless confusion, as will be readily understood.

In other systems, in which sensitive electromagnetic devices are employed, such as polarized relays, neutral relays, etc., the difliculties met with are usually of another kind, but are no less serious. In such cases it frequently happens that the sensitive devices are affected by stray currents from exter-' nal sources, or by induction therefrom, and

their operation is impaired to such an extent as to make them practically inoperative. The large number of electric railways, and transmission circuits of other kinds, now in use, especially in the vicinity of large cities and towns where multiplex telegraphy is of greatest value, make such stray and induced currents too prevalent for the commercial use of multiplex systems, of the kind just described.

I have therefore been led -to devise my present invention, in which I employ a telephone current, that is, a pulsating current, in contradistinction to a Morse or intermittent current. I have found that a telephone circuit is not so affected by external currents as to obliterate the characteristics of the pulsations therein, so that it may still be used, in connection with proper devices,

time element in the successive makes and breaks thus produced is not, to a certain ex tent at least, a material factor in the operation of the telephonic system.

In carrying out my invention I utilize, as

IIO

before stated, a telephone circuit, including suitable receiving and transmitting devices. At the latter are produced sounds, as, for example, musical notes, representing certain letters, words or other symbols, etc. At the receiver the sounds are recognized by their characteristics, as pitch, duration, change of pitch or duration, etc, according to a prearranged code. For the purpose of connecting the transmitting stations with their respective receivers, each. of the former may be connected with one of a series of contacts, over which passes a brush connected through the line wire with a similar brush or trailer moving in unison over a similar series of contacts to which the receiving stations are connected. By this means the receiving devices are connected with the linein rapid succession, as many times per second as may be necessary. As the independently variable factor which affects the current is pitch (that is, the number of pulsations or waves in a unit of time), and not the make and break of the circuit,the interruption of the current by the moving member or contact has no ultimate effect at the receiving end. As a matter of fact the current which affects the diaphragm of the receiver will be regularly intermittent, but its rate of pulsation is not. altered thereby. Consequently, the dia phragm itself may vibrate int-ermittently,- in other words, the sound waves projected thereby may be produced in series, so that the tone would in reality be a rapid succession of tones of the same pitch. However, the tone may be identified, irrespective of its time. For example, instead of being a whole note, of a given duration, the sound actually perceived by the operation may be two or more quarter notes, or eights, sixteenths, etc. On the other hand, the rotation of the moving contact may be slow enough to leave a considerable interval between successive connection ofthe same with the successive receiving and sending instruments. In such case the sending operator, having depressed his key or otherwise caused a tone to be uttered into his transmitter, listens until he hears the tone in his own receiver. \Vhereupon he knows that his transmitter is in connection with the corresponding receiver at the other end of the line and that the tone is likewise audible there. As soon as he ceases to hear the tone he knows that his circuit is broken and he at once depresses another key and holds it till he hears the tone in his receiver. .[n this w y the entire message may be sent, but it will be noted that the speed of the transmission thereof corresponds exactly with the speed of the revolving contact. That is, only so many tones are sent per unit of time as there are successive connections of the particular circuit in the same period. Of course, if the duration of each connection is long enough,

two or more tones may be sent before the connection is broken. In any case the tone or tones sent may be made as much shorter in time than the duration of the connection as may be desired.

Recognizing the tone, the operator may translate the same into the corresponding letter or symbol. When he perceives a change of pitch he translates this into its corresponding symbol, and so on. The changes of pitch of course originate at the transmitting end of the circuit, and may be effected by playing upon a pipe, a string, or the human voice itself may furnish the tones.

A person having a highly trained musical ear may be able to distinguish and name any note in the scale of an ordinary piano instantly upon hearing it, even when it is not preceded or followed by other notes. It is thus possible to give each letter of the alphabet a different note, which will be recognized and translated by the receiving operaton Practically, however, it will be found better to use fewer tones, and to represent some of the letters by combinations of these tones. Many persons are able to distinguish and name the seven notes of the major scale, and most persons may learn, without great effort, to 'doso. A code based on such notes might be arranged by assigning the seven tones to as many of the more frequently used letters:

For example, the key-note, or tonic, do, may represent the letter 6. may indicate a, etc. When the seven notes have thus been usedlsingly they maybe combined. Thus, do followed. by re may represent a letter, as I); do followed by mi, 0, do followed by fa, d; re followed by at, w; etc. In this way a complete code may be constructed.

Instead of using the whole scale, (seven notes) fewer tones may be. used, combined in threes. 'lhus, do-re-mimay represent the letter do-re-sol, the letter It; etc. way, simply by permntating notes in. groups of two or more, as many different characters or symbols may be represented as desired. The intensity of the tones may also be used as a characteristic. Thus, a loud (to followed by do less loud, may represent a certain letter, while do loud, followed by re less loud, may represent another, etc. Duration or time may also be used as a distinguishing characteristic. -Thus a long (to might represent a certain letter, while the same note, but of shorter duration, might represent another. By combining the same note in periods of different length a code similar to the ordinary I\lorse alphabet may be arranged, using for that purpose a single tone; of anypitch. For example, a short note may represent a; a long note followed by a shorter one, 7), etc. Time. and pitch may alsobc combined, making it easier to distinguish the differentcharacteristics which indicate the letters. Then certain The next note, re, 7

In this,

. is of course clear that other arrangementshears a long note he at once knows ,that some .code, and not only is the readiness of recogniletters may be represented by combinations of long notes. Hearing 0. long note the signal is at once localized within known limits by the receiving operator, and the final determination of the signal is correspomlingly simplified. For example, a, I), c, (I, a, may be rcpresented as follows: the other letters being all represented by combinations beginning with short notes. Hence when the operator one ofthe letter just named is being sent. His attention is therefore coniined at on e to only live combinations in that particular tion thereby increased, but the liability of error is decreased.

The above methods of arranging codes are given merely as illustrative examples, and it may be used, as desired.

A simple embodiment of my invention is shown in the accompanying drawings, in which Figure 1 is a (.iagram showing the entire system, and Fig. 2 is a view showing the manner of operating the rotating contaits in synchronism.

The system of Fig. 1 shows four stations, A, B, C, D, but obviously more or less than that number may be employed if desired. T, T, T indicate the transmitting; telephones, shown as ordinary magneto instruments. Any other suitable type may of course be used, as convenient. Connected therewith in the manner shown are the fixed contacts of the make-and-break devices M, M, whose revolving contacts or trailers t, t, are connected by a line wire L. With the trailers in the positions shown, the stations A and C are connected, and may be sending and receiving as long as the trailers remain in the corresponding contacts. When the trailers move upon the other contacts the stations mentioned are disconnected and the stations B, D, are put into communication With each other.

In series with the transmitters and their corresponding fixed contacts are receivers R, R, R R so that each operator may hear his own signals and those coming from the other station.

P, P, P, I? are pipes or other devices for producing sounds.

As before stated, the trailers are revolved in synchronism. Any suitable means for effecting this operation may be used, as for example the devices shown in Fig. 2. G indicates an alternating current generator con- 1 nected to the line L through an inductive resistance r, and to the ground at g. The trailer tis mounted on the shaft 8 of the generator, so that the movement of the trailer over the contact ring 0 bears an absolutely fixed relation to the current charges in the. line. The other trailer, t, is mounted on a l shaft which is independently driven by a suitable motor, as the clockwork indicated by ll, and which also bears a scape wheel 10. The latter is controlled by a pivoted lever Z, carrying the usual pallets. 'l'he lever Z constitutes the armature ot a polarized relay p and carries a magnet coil m, connected to the line L through an inductive resistance r, and to the ground at g. As the armature vibrates, on account of its changing polarity, the escape wheel is permitted to rotate stepbystep, and with it the trailer t. The various parts of the escapement devices may be so constructed, as will be understood by those skilled in the art, that the trailer 25. will revolve in unison with the trailer t, though the movement of tlie lat-ter is of course continuous while the former moves stepbystcp. I prefer to use a generator current of comparatively low frequency, as such a current may be prevented from reaching the telephones by condensers b, which of course permit the high frequency telephone currents to pass through them to the line. On the other hand the resistances r, 1", confine the telephone currents to the line.

A method of signaling by means of the above apparatus mav now be described in detail, as follows: lqet it be supposed that the trailers are revolving at a rate of eight complete revolutions per second, making eight connections of station A with C and B with D, in that unit of time. Each period of connection will be one-sixteenth of a second, followed by a break of the same duration. Suppose that the operators at A and B are each sounding a note. The former hears his tone .in his receiver R as long as the trailers are on the right hand contacts. As soon as he ceases to hear the tone he knows that the operator at C also ceases to hear it.. A then produces another tone, and continues so until he hears it in his receiver. At the sameinstant it is heard by C, who translates it into the proper symbol or waits for such further tones from A as may be necessary to complete the signal. Between each letter or symbol the sending operator may omit to send a tone, thereby making it clear to C that the letter is complete. \Vhile A and C are thus signaling, B and D may do the same, though it will of course be understood that the tones or sounds between the latter stations are sent during the intervals of the tones or sounds between A and C, and vice versa.

In the above method the number of tones sent by a station is the same as the number of connections per second, that is, eight. Practice may make the operators expert enough to send and receive two tones in each period of contact, thus doubling the speed of the work. \Vith codes in which no letter is represented by more than two tones, it may be desirable to transmit both tones in a single IlO period, so that the succeeding break will always indicate the completion of a letter. The speed of the trailers may of course be regulated, if necessary, to permit such a method to be employed. On the other hand the speed of the trailers may be made so high that the interval of break is so short as to be negligible. For example, suppose the rate to be thirty-two per second, making thirtytwo connections of A with C and B with D, each one sixty-fourth of a second long and each followed by a break of the same duration. If now A sounds a tone, he and C will,

as long as the tone continues, hear it as a succession of short tones or a continuous tone of regularly varyin loudness. Obviously, under such conditlons, the tone may be changed at will by the sending operator Without regard to the make and break of the circuit. I

From the fore oing it will beseen that my invention provi es a simple multiplex system in which the determinative characteristics of the current employed are not obliterated by the extraneous influences which make the prior multiplex systems inoperative. My system is in fact as reliable as a single-message telephone circuit. It is also inexpensive to install, as the apparatus is very simple, and can be maintained at slight cost.

The invention is of course capable of various embodiments, and that shown and described herein is merely a typical form.

What I claim is:

1. In a system of multiplex telegraphy, the combination of a plurality of telephone instruments, means at each telephone transmitter for delivering thereto inarticulate tones representing letters or othersymbols according to a prearranged code, and means for connecting the telephones groups at regularly recurring intervals, as set forth.

2. In a system of multiplex tele raphy, the combination of a plurality of te e hone instruments, a common transmission circuit therefor, means at each telephone transmitter for delivering thereto inarticulate tones representing letters or other symbols according to a prearranged code, and means for connecting the telephones to the said circuit in groups at regularly recurring intervals,- as set forth.

3. In a system of multiplex telegraphy, the combination of a series of insulated contacts, telephone instruments connected with the contacts, a similar series of contacts and telephone instruments connected therewith,

electrically connected trailers moving over the series of contacts in unison to connect the telephones in groups, and means at each telephone transmitter for deliverin thereto inarticulate tones corresponding to Ietters or other symbols according to a prearranged code, as set forth.

4. The combination with a plurality of telephone instruments; of means for connecting the instruments in groups, comprising two circular series of insulated contacts to which the instruments are connected, each series being provided with a revolving contact; a line conductor connecting the contact; a generator carrying one of the movable contacts on its rotating element, and connected to deliver its current to the line conductor; a step-by-step motor for actuating the other revolving contact, under the control of the current from the generator, as set forth.

JOHN BURRY.

Witnesses:

M. LAWSON DYER, S. S. DUNHAM. 

